MUTATIONS: SENTENCE ANALOGIES

Consider the following sentence made up of three letter words. The words represent what will eventually be codons in a strand of mRNA: if the bases in the codons are in the correct sequence, the proper protein is made, just as if the letters are in the correct sequence, the sentence makes sense and isn't a bunch of jibberish.

The bad cat saw the big dog and ran and bit him

INSERTION MUTATION ANALOGY

If another fragment of DNA (with the sequence inserted dna) were to insert itself into a point in the original strand, it is likely that an abnormal protein will be made (the sentence will no longer make sense):

The bad cat sai nse rte ddn awt heb igd oga ndr ana ndb ith im

DELETION MUTATION ANALOGY

"Spelling" isn't the only concern either. The syntax of the sentence must make sense as well. So just as inserting large pieces of DNA into a strand usually prevents a normal protein from being made, so will the deletion of large fragments of the original strand. Consider our example sentence again:

The bad and ran and bit him

Although this sentence is spelled correctly (ie, "in frame"), it makes no sense because it's missing the words in the middle. Likewise, such a deletion in DNA would lead to a protein missing many of its amino acids, and will most likely not be functional.

POINT MUTATIONS ANALOGIES

Now that we've discussed insertions and deletions, consider the effects of point mutations. Point mutations can do one of three things:

give rise to the same amino acid (or "word" in our example) as originally intended, leaving no indication that mutation occurred; this is called SAME-SENSE
The bad cat sAw the big dog and ran and bit him
give rise to a different amino acid than originally intended, which may or may not lead to a functional protein depending on the role of that amino acid; this is called MIS-SENSE
The bad cat sew the big dog and ran and bit him
give rise to a premature termination signal, leading to a truncated protein; this is called NON-SENSE
The bad cat s.w the big dog and ran and bit him

Contributed by Deanna Raineri